Methods of blood correction are known and widely used in particular for treatment of patients suffering from kidney and/or liver diseases. One of the conventional techniques, known as haemo- or lymph-perfusion, is based on passing the blood or lymph through an adsorbent such as granular activated carbon. Unfortunately, a relatively large amount of biological fluid, namely about 250-300 ml, is withdrawn from the patient's body at any given time and a duration of the whole process of purification is more than 2 hours. Actually, the carbon loses its effectiveness after 15-20 minutes from the beginning of the treatment because it slimes and, owing to the relatively large dimensions of the carbon particles, becomes formed with numerous channels which are formed therein by the blood during its passage therethrough. As a result, unpurified blood returns into the body.
Another conventional technique, known as haemodialysis, is based on the use of semipermeable membranes. Similarly to the haemoperfusion, this method also requires the withdrawal of about 400-600 ml of blood at any given time and more than 4 hours for the whole process of purification, wherein the blood passes through the apparatus typically more than 5 times. Both of the above described techniques disturb the blood's rheology. That is to say they traumatize the erythrocytes and thrombocytes. They also require bulky equipment.
Methods and devices for blood purification have been developed employing the so called haemoseparation technique which is based on the principles of magnetic separation. Generally, the magnetic separation procedure consists of retaining magnetic materials in a chamber disposed in a magnetic field. Systems of this kind typically provide mixing of the blood with a previously prepared magneto-conductive substance formed of paramagnetic beads having a coating which selectively binds a preselected pathogenic agent or endotoxin. Then, by passing a blood mixture containing the paramagnetic beads having the bound pathogenic agent through a magnetic field, the paramagnetic beads are magnetically separated from the blood.
U.S. Pat. No. 5,123,901 discloses a method and an apparatus for removing preselected cells or viruses from the blood. The blood is first tested for selection a preselected pathogenic agent and identifying an associated antigenic agent. A composition is then prepared, such as an immunoglobulin or an antibody, for coating a plurality of paramagnetic beads with outer layers so as to recognize and bind selectively to the preselected pathogenic agent. The paramagnetic beads have a smooth surface in order to minimize the amount of antibody necessary to coat the beads. The blood is perfused into a flow line and the coated paramagnetic beads are metered into the blood either before entering by the latter a mixing coil, or thereafter. A received mixture of blood and paramagnetic beads/pathogenic agent complexes flows into a chamber of a magnetic separator. A graded magnetic field is provided along the length of the separation chamber so as to adhere substantially all of the paramagnetic beads/pathogenic agent complexes to the separation chamber wall. However, both the mixing chamber and the separation chamber are bulky, namely each about 300 cm in length. About 600 to 700 ml of blood occupies the flow circuit at any given time, while the purging process is completed in approximately 6 to 10 hours of operation. Additionally, the magnetic field is graded such that it begins at 4,000 Gauss (0.4 T) and increases to about 10,000 Gauss (1 T), which is too much for such a biological fluid as blood. Indeed, it is known in the art that the magnetic field intensity which is suitable for intervention into a biological fluid is defined by the properties of the latter. This is more essential for such a multicomponent biological fluid as blood containing crythrocytes whose equidistance increases and membrane resistivity decreases with the increase of the magnetic field. As a result, the erythro-cytes grow old and break.
PCT Publication No. WO 94/21310 discloses a method and an apparatus for correcting a biological fluid typically based on mixing the latter with a biocompatible suspension of a magneto-conductive composition within a mixing chamber and, then, passing the obtained mixture through a filter disposed within a magnetic field. The biological fluid is corrected in a number of cycles. In order to provide more effective mixing, the mixing chamber is filled in with discrete doses of the biological fluid and the suspension of the magneto-conductive composition. The obtained mixture is left standing whilst being continuously mixed, and, then, each further dose is added to the previously obtained mixture. Then, the resulting mixture passes through a filter disposed in a magnetic field effect region. The time of passage of the mixture through the filter is preset so as to achieve an optimum effect in the magnetic field which does not exceed 120 mT. Unfortunately, such procedure is slow, requiring that about 100 ml of the biological fluid be withdrawn from the body during a cycle and resulting in about 10 hours of operation for complete correction of the whole amount of the patient's blood.
It should be noted that such parameters as the amount of biological fluid which is withdrawn from the patient's body at any given time and the duration of the whole treatment are very important and even determinant when dealing with endotoxic and/or exotoxic shocks which are usually caused by poisoning.